This invention relates to a control device for motor/generators used in a hybrid vehicle.
One type of hybrid vehicle mounts two motor/generators. One of the motor/generators is used for running the vehicle (hereafter referred to as xe2x80x9cthe vehicle-running motor/generatorxe2x80x9d) with the other being used for the generation of electrical power (hereafter referred to as xe2x80x9cthe power-generating motor/generatorxe2x80x9d). The two motor/generators are operated by a common direct-current power source. An inverter and a circuit generating a pulse width modulation (PWM) signal are provided in each of the motor/generators. The vehicle-running motor/generator is rotated and driven by an alternating current converted from the direct current by the inverter. The power-generating motor/generator is rotated by the prime mover, that is to say, by the engine and generates an alternating current. The resulting alternating current is converted to a direct current and stored in a battery by switching elements of the inverter.
Since the switching elements of the inverter which drives the AC motor perform switching operations at high frequencies of 10-20 kHz, high frequency electrical noise is generated by a pulse-shaped ripple current generated in the DC bus lines.
As a result, a solution is required for the detrimental effects of such high frequency noise on nearby electrical components. Normally a noise-reducing reactor functioning as a noise filter or a smoothing electrolytic condenser which can resist large ripple currents is disposed between the switching circuit of the inverter and the DC power source. However since this solution requires the use of large components such as a large capacity reactor and an electrolytic condenser, problems arise which are related to weight increases and the fact that the size of the inverter case must be increased. The above problem is exacerbated by the fact that as stated above two or more inverters are mounted in a hybrid automobile.
Tokkai 2000-78850 published by the Japanese Patent Office in 2000 discloses a controller for motor/generators which suppresses ripple current by shifting the ON-OFF timing of the switching element.
However since pulses generated by the vehicle-running motor/generator and pulses in the opposite direction generated by the power-generating motor/generator are alternately applied to the DC bus lines, it is not possible for the controller to effectively reduce ripple currents resulting in high-frequency electrical noise.
This invention has the object of providing a control device for motor/generators which effectively reduces ripple current. In order to achieve above objects, this invention provides a control device for motor/generators.
The control device for motor/generators comprises; a first inverter connected to a direct-current (DC) power source through DC bus lines, the first inverter applying a control current to a first motor/generator which is used mainly as a motor; a second inverter connected to the direct-current power source through the DC bus lines, the second inverter applying a control current to a second motor/generator which is used mainly as a generator, the second inverter having the same configuration of switching elements as the first inverter; a first PWM signal generating circuit comparing a first carrier signal limiting the operational frequency of the first inverter with a first voltage command signal for establishing a desired control current of the first motor/generator, the first PWM signal generating circuit generating pulse width modulation (PWM) signals each operating one of the switching elements of the first inverter; and a second PWM signal generating circuit for comparing a second carrier signal with a second voltage command signal and generating pulse width modulation (PWM) signals each operating one of switching elements of the second inverter, the second carrier signal having the same period as the first carrier signal and limiting the operational frequency of the second inverter, the second voltage command signal establishing a desired control current of the second motor/generator.
The first PWM signal generating circuit and the second PWM signal generating circuit control the first inverter and the second inverter respectively so that the operation of the first inverter is synchronized with the operation of the second inverter and so that the current of the first inverter which flows in the DC bus lines flows in an opposite direction to the current of the second inverter which flows in the DC bus line.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.